When you think those markers are too dried out to use you can make watercolor paint.
In this example small jars were used and water added to the jars just below the area for the screw top. It’s best to leave the markers for at least 8 hours, and the consistency of your watercolors will depend on the amount of water, the amount of ink in the markers, and how long you let them drain.
Once they’re ready, just cap the jars and give a good shake before use. Not really artist level watercolors but great for those rainy day projects.
Easy and cheap.